Retrieving the effective radius of Saharan dust coarse mode from AIRS observations
Clémence Pierangelo(1), Michael Mishchenko(2), Yves Balkanski(3) and Alain Chédin(1)
(1)Laboratoire de Météorologie Dynamique/IPSL,
(2)Goddard Institute for Space Studies/NASA,
(3)Laboratoire des Sciences du Climat et de l'Environnement/IPSL
XIV International TOVS Study Conference, China, 25-31 May 2005
Dust size distribution constitutes a key parameter to assess clear-sky shortwave aerosol radiative forcing. A large number of in-situ or remote sensing experiments have been developed to retrieve information on this key parameter. In this study, we show that the effective radius of dust coarse mode can be retrieved from Aqua/Advanced Infrared Sounder (AIRS) observations, with a two step process. First, for each AIRS observation, the dust infrared optical depth, the mean altitude of the dust layer and an estimate of the temperature and water vapor tropospheric profiles are obtained from 8 channels, using a Look-Up-Table approach. Second, once these parameters are determined, the effective radius is retrieved from an additional AIRS channel, sensitive to dust size and not to ozone variations or dust shape (channel 165: 1072.5 cm-1 or 9.32 μm). We present a comparison between dust coarse mode effective radius retrieved from AIRS over the Atlantic Ocean for the period April to June 2003 and in-situ measurements, General Circulation Model simulations and sun-photometer retrievals. We determine from our retrieval that the coarse mode effective radius decreases with transport, from 2.4 μm near the African coast to 1.9 μm over the Caribbean islands.